bnxt: fill data page pool with frags if PAGE_SIZE > BNXT_RX_PAGE_SIZE

The data page pool always fills the HW rx ring with pages. On arm64 with
64K pages, this will waste _at least_ 32K of memory per entry in the rx
ring.

Fix by fragmenting the pages if PAGE_SIZE > BNXT_RX_PAGE_SIZE. This
makes the data page pool the same as the header pool.

Tested with iperf3 with a small (64 entries) rx ring to encourage buffer
circulation.

Fixes: cd1fafe7da1f ("eth: bnxt: add support rx side device memory TCP")
Reviewed-by: Michael Chan <[e-mail]>
Signed-off-by: David Wei <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/broadcom/bnxt/bnxt.c

···
 
 static netmem_ref __bnxt_alloc_rx_netmem(struct bnxt *bp, dma_addr_t *mapping,
 					 struct bnxt_rx_ring_info *rxr,
+					 unsigned int *offset,
 					 gfp_t gfp)
 {
 	netmem_ref netmem;
 
-	netmem = page_pool_alloc_netmems(rxr->page_pool, gfp);
+	if (PAGE_SIZE > BNXT_RX_PAGE_SIZE) {
+		netmem = page_pool_alloc_frag_netmem(rxr->page_pool, offset, BNXT_RX_PAGE_SIZE, gfp);
+	} else {
+		netmem = page_pool_alloc_netmems(rxr->page_pool, gfp);
+		*offset = 0;
+	}
 	if (!netmem)
 		return 0;
 
-	*mapping = page_pool_get_dma_addr_netmem(netmem);
+	*mapping = page_pool_get_dma_addr_netmem(netmem) + *offset;
 	return netmem;
 }
 
···
 	dma_addr_t mapping;
 	netmem_ref netmem;
 
-	netmem = __bnxt_alloc_rx_netmem(bp, &mapping, rxr, gfp);
+	netmem = __bnxt_alloc_rx_netmem(bp, &mapping, rxr, &offset, gfp);
 	if (!netmem)
 		return -ENOMEM;